The present invention relates to a multilayered circuit board for a semiconductor chip module and, more particularly, to a multilayered circuit board for a semiconductor chip module suitable for high-density wiring.
Recently in a multilayered circuit board for a semiconductor chip module, the semiconductor chip module having a plurality of IC chips is mounted on the die pad of a lead frame. The electrodes between the IC chips mounted on the lead frame and the multilayered circuit board, the lead frame, and the semiconductor chip module board are electrically connected by bumps or wire bonding.
The mainstream of such multilayered circuit boards is a resin-layered board prepared by forming a thin-film multilayered circuit of copper and polyimide on an underlying board of ceramics or the like.
FIGS. 7A and 7B show an example of a conventional multilayered circuit board for a semiconductor chip module. FIG. 7A shows the whole structure, and FIG. 7B shows a section taken along the line Axe2x80x94A in FIG. 7A.
As shown in FIG. 7A, a semiconductor chip 9 and chip component 8 are mounted on a conventional multilayered circuit board 11 for a semiconductor chip module. The semiconductor chip 9 and chip component 8 are connected by bonding wires 10, GND wiring layers 14 on the board surface, and metallized portions 12 at the board edge to the GND terminal (not shown) of a motherboard on which the multilayered circuit board 11 is mounted.
In the conventional board structure, a current to the GND terminal flows from the semiconductor chip 9 to the GND terminal of the motherboard through the bonding wire 10, chip component 8, GND wiring layer 14, metallized portion 12, and lead wire 13, as indicated by the arrows in FIG. 7B. The metallized portion 12 which passes a current to the GND terminal is formed at the peripheral portion of the multilayered circuit board 11. The GND wiring layer 14 must be extended to the metallized portion 12 at the peripheral portion, which prolongs the GND wiring layer 14.
In the conventional multilayered circuit board for a semiconductor chip module, the long GND wiring layer increases the resistance and impedance of the GND wiring layer, and a potential higher than the correct GND potential is undesirably supplied to the semiconductor chip. The long GND wiring layer also increases power consumption.
It is, therefore, a principal object of the present invention to shorten the GND wiring layer of a multilayered circuit board for a semiconductor chip module suitably for high-density wiring.
To achieve the above object, according to the present invention, there is provided a multilayered circuit board for a semiconductor chip module, comprising an underlying board having a major surface made of a metal material to which a fixed potential is applied, insulating layers which are stacked on the major surface of the underlying board and have wiring layers formed on surfaces of the insulating layers, fixed-potential wiring layers constituting part of the wiring layers formed on the insulating layers, via holes formed below the fixed-potential wiring layers to extend through the insulating layers, and metal layers filled in the via holes so as to make upper ends be connected to lower surfaces of the fixed-potential wiring layers, wherein one of the insulating layers in contact with the major surface of the underlying board is formed on the underlying board while a lower end of the metal layer is in contact with the major surface of the underlying board, and the other insulating layer formed on the insulating layer in contact with the major surface of the underlying board is stacked while a lower end of the metal layer is in contact with an upper surface of the fixed-potential wiring layer of the one insulating layer.